A bag of chips here, a flavored yogurt there, a frozen meal on a busy night. For many adults over 40, ultra-processed foods quietly account for about 41% of daily calories. According to a study published in April 2026, that level of intake is tied to measurably worse performance on tests of visual attention and mental processing speed, even when the rest of the diet looks reasonably healthy.
The research, led by a team at Monash University in Australia and published in Alzheimer’s & Dementia: Diagnosis, Assessment & Disease Monitoring, tested middle-aged and older adults using the Cogstate Brief Battery, a set of computerized tasks that measure how quickly the brain detects and responds to visual information. For every 10% increase in daily energy from ultra-processed foods, participants scored lower on attention and speed tasks. The researchers controlled for overall diet quality, meaning the association held regardless of whether someone also ate plenty of fruits and vegetables.
What the numbers actually show
The study used the NOVA classification system, which sorts foods into four groups based on how much industrial processing they undergo. Group 4, the ultra-processed category, includes products like soft drinks, packaged snacks, instant noodles, reconstituted meat products, and many breakfast cereals. These items typically contain ingredients rarely found in home kitchens: emulsifiers, flavor enhancers, hydrogenated oils, and high-fructose corn syrup.
Across the Australian cohort, the average participant got roughly 41% of their energy from these Group 4 foods. That figure is consistent with dietary surveys from the United States, the United Kingdom, and Canada, where ultra-processed products dominate supermarket shelves and account for a similar share of national calorie intake.
The cognitive tests were specific. The Cogstate Brief Battery asks participants to respond as quickly and accurately as possible to visual cues on a screen, capturing reaction time in milliseconds. These are not memory quizzes or vocabulary tests. They measure the kind of rapid visual processing people rely on when driving, scanning a crowded room, or following a fast-moving conversation. The finding that ultra-processed food intake tracked with slower performance on these particular tasks suggests the association is not about general intelligence but about the brain’s speed and sharpness in real time.
Consistent patterns across countries
The Australian results do not stand alone. A separate analysis of the U.S. National Health and Nutrition Examination Survey (NHANES), covering 2011 to 2014, found a similar pattern among older American adults. That study used the Digit Symbol Substitution Test, a pen-and-paper measure of processing speed in which participants match symbols to numbers under time pressure. Higher ultra-processed food consumption was associated with slower scores.
Having two independent populations, tested with different cognitive instruments, point in the same direction makes it harder to dismiss the association as a quirk of one dataset or one measurement tool.
Data from the Framingham Heart Study, one of the longest-running cardiovascular and brain health studies in the United States, extends the picture further. Prospective analyses from that cohort have linked daily ultra-processed food servings to increased risk of Alzheimer’s disease over follow-up periods spanning years, not just a single snapshot. While the Framingham work focuses on dementia incidence rather than processing speed, it suggests the cognitive consequences of ultra-processed diets may compound over time.
European evidence adds nuance. A cohort analysis published in the European Journal of Nutrition examined ultra-processed food intake and cognitive decline across different age groups and follow-up periods. Its findings were broadly consistent with the Australian and American data on processing speed and executive function but more mixed when it came to memory. That unevenness is worth noting: the relationship between diet and cognition may not affect all mental abilities equally.
Why this is not yet a proven cause
Both the Australian and the NHANES studies are cross-sectional. They captured diet and cognition at a single point in time, which means they can identify associations but cannot prove that ultra-processed foods directly caused the slower test scores. People who eat more packaged food may also sleep less, exercise less, experience more stress, or face socioeconomic pressures that independently affect brain function. The researchers adjusted for several of these factors, including overall diet quality, but no observational study can account for every possible confounder.
The European cohort study partially addresses this limitation by following participants over multiple years, but its mixed results across cognitive domains suggest the picture is more complicated than a single headline can capture. No large, diverse study has yet tracked participants from a baseline diet through years of detailed cognitive testing to confirm a clear dose-response curve for attention and visual processing specifically.
The biological mechanisms remain plausible but unproven in humans. Ultra-processed meals tend to be softer and eaten faster, leading to higher calorie intake compared with minimally processed meals matched for the same nutrients, as demonstrated in a controlled feeding study at the National Institutes of Health. That overconsumption could feed into chronic inflammation, insulin resistance, and vascular damage, all of which are known to affect the brain. Additives and emulsifiers may also alter the gut microbiome in ways that influence neurological function, but direct human evidence for these pathways is still thin.
No published randomized trial has yet measured what happens to attention, reaction time, or brain imaging markers when people switch from an ultra-processed diet to a minimally processed one. Until that kind of evidence exists, the strongest honest statement is that high ultra-processed food intake is a plausible and modifiable risk factor for slower cognitive processing, not a confirmed cause.
What this means at the grocery store
For people who want to act on the available evidence without waiting for a perfect trial, the practical steps are straightforward. Swapping a packet of chips for whole fruit or a handful of nuts, choosing plain yogurt over a flavored variety loaded with added sugars, or cooking a simple meal from basic ingredients instead of reheating a frozen entree are all changes that reduce ultra-processed food intake. These substitutions also carry well-established benefits for heart health, blood sugar regulation, and weight management, so the potential upside extends well beyond cognition.
That said, ultra-processed foods are a broad category. A can of soda and a fortified whole-grain cereal both fall under NOVA Group 4, despite having very different nutrient profiles. Time, income, and access to fresh food all shape how realistic it is for any individual to overhaul their diet. Framing ultra-processed food as a single villain oversimplifies a problem that is partly about food systems, partly about individual choices, and partly about gaps in the science.
Where the research goes next
The clearest gap in the evidence is the absence of randomized controlled trials designed around cognitive endpoints. Researchers would need to assign participants to diets that differ primarily in processing level, hold calories and nutrients constant, and then measure attention, reaction time, and brain function over weeks or months. That kind of study is expensive and logistically demanding, but it is the only way to move from association to causation.
Longer-term cohort studies that combine dietary tracking with repeated cognitive testing and brain imaging would also help clarify whether the association seen in cross-sectional data holds up over time and whether certain subgroups, defined by age, sex, genetics, or baseline health, are more vulnerable than others. Until those studies are completed, the current evidence offers a consistent and concerning signal: the more ultra-processed food people eat, the slower their brains appear to work on tasks that demand quick, accurate visual attention.
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*This article was researched with the help of AI, with human editors creating the final content.
